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The Secret to Happiness Can Be Found by Digging in the Dirt

By Anna North August 31, 2014 11:10 amAugust 31, 2014 11:10 am

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Credit Erich Schlegel for The New York Times

By now, many of us are familiar with the “hygiene hypothesis” — the idea that an environment that’s too clean may actually increase our risk of disease. This hypothesis usually gets discussed in terms of ailments like allergies or autoimmune disorders, but some research shows that dirt might be good for our mental health, too.

At Modern Farmer, Anna Brones talks to Christopher Lowry, a professor of physiology who’s studied the effects of a particular soil bacterium on mouse brains. He says that bacteria like this could one day help treat diseases involving inflammation — and that inflammation is associated not just with physical ills but also with psychiatric ones like PTSD and major depression. Graham Rook, a microbiology professor who worked with Mr. Lowry, explains to Ms. Brones that “people usually assume that the health benefits of exposure to green space are due to exercise” but that “contact with microbial biodiversity is looking like the most probable explanation for the green space effect.”

Mr. Rook’s and Mr. Lowry’s research, Ms. Brones writes, “gives us a better understanding of exactly why being outside, in a garden or on a farm, makes us feel good.”

Researchers aren’t sure, she notes, how much gardening (or other dirt-centric activities) you need to do in order to feel happier. However, she cites a 2007 Discover piece whose headline goes so far as to ask, “Is Dirt the New Prozac?” Mr. Lowry tells Discover the bacteria he studied “had the exact same effect as antidepressant drugs” on mice. And Mr. Rook says, “It’s not clear to me whether the way ahead will be drugs that circumvent the use of these bugs, or whether it will be easier to say, ‘The hell with it, let’s use the bugs.’”

In an April piece at Backcountry.com, Danielle Mariott rejoices at the dirt-happiness connection:

“You know what rules most about this? You can ditch that dumb hand sanitizer dongle and just go about your day. These studies suggest that an imbalance of the immune system can lead to depression and that a certain soil bacterium might be the cure. So, basically, get outside, get in the dirt, get happy.”

Still, Prozac made of dirt (or just the “bugs” from the dirt) may not be in our immediate future. The hygiene hypothesis has seen some criticism — in a 2011 Scientific American article, Veronique Greenwood writes that while the hypothesis was initially thought to explain rising rates of asthma, recent research calls this explanation into question. She explains:

“Children in Latin America with high rates of supposedly protective infection have even higher rates of asthma than children in western Europe. Inner-city children in Chicago and New York have quite high rates of asthma, despite unhygienic living. And the rates of asthma varied among countries with very similar histories of cleanliness — indicating that there was more to it than tidiness.”

She concludes:

“It will take years to understand fully whether microbial exposure, lifestyle changes or the obesity epidemic is more important in explaining the continuing increase in asthma rates. But one thing is clear: the hygiene hypothesis was just the beginning.”

And in a New York Times review of Moises Velasquez-Manoff’s book on the hypothesis, “An Epidemic of Absence,” Dr. Abigail Zuger takes a somewhat dim view of patients’ attempts to take matters into their own hands:

“Scientists are now beginning to treat various illnesses with probiotics, various combinations of ‘good’ intestinal bacteria. So far results are mixed: some good, some inconclusive.

“Enthusiastic patients, however, enabled by the usual cast of shady entrepreneurs, have predictably skipped the long, dull validation process and are busily infecting themselves with a variety of intestinal worms.”

It may be a long while before researchers fully understand the relationship between cleanliness and health — Ms. Greenwood notes that “a reworking of the hygiene hypothesis that focuses on changes in the normal nondisease-causing bacteria that live inside and on the body (in the intestines or the airways or on the skin) has promise.” But even if dirt doesn’t cure clinical depression, some ways of getting dirty may provide a little mood boost. Ms. Mariott writes:

“I say, next time you’re on a trail, don’t run like you’re afraid to mess up your hair. Run like you’re a kid again, and biff it — just so you can laugh and get a good dose of dirt.”

Whether or not it’s healthy, worrying a little less about getting dirty might at least be fun.

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